1. Field of the Invention
The present invention relates to an improved digital gas detecting device for detecting a pollution level of the air in the vicinity of a vehicle and controlling a ventilation system of the vehicle, and more particularly, to a gas detecting sensor having a novel structure for detecting concentrations of a gasoline gas and a diesel gas and a gas detecting device for estimating a pollution level of the air around a vehicle using the gas detecting sensor and controlling a ventilation system.
2. Description of Related Art
A typical gas detecting sensor is a semiconductor sensor using tin dioxide as an active layer. This typical gas detecting sensor has a defect that it cannot sense two kinds of exhaust gases generated by a gasoline vehicle and a diesel vehicle all together. To sense both exhaust gases together, two sensors should be used. A tin dioxide (SnO.sub.2) sensor is used to detect the gasoline exhaust gas and a tungsten trioxide (WO.sub.3) sensor is used to detect the diesel exhaust gas. However, if two sensors are used, a sensor installation structure and a sensing circuit should be constituted in dual, thereby increasing the size and cost of the gas detecting device.
There have been provided with gas detecting sensors doped with sensing material comprising a compound of various metallic oxides, for detecting gases based upon increase/decrease of resistance caused by the effects of typical gases. However, when only one sensor is used, it is difficult to separate a sensor signal generated due to gasoline exhaust gas from a sensor signal generated due to diesel gas exhaust gas. Besides, complicated sensor signal conversion and signal processing is required. Moreover, when using the sensor having a metallic oxide compound, it may happen that the sensor wrongly senses polluted air and performs a wrong operation with respect to the ventilation system if very harmful material has influenced the sensor device at constant concentration for a long time, for example, if the vehicle has been parked in a very polluted underground parking lot for a long time.